1. Technical Field
The present invention relates to an etching apparatus, and in particular to an etching apparatus selectively etching the peripheral portion of the wafer.
2. Related Art
In fabrication process of semiconductor devices, it is necessary to remove metal or other contaminants adhered to the peripheral portion of wafers, in order to avoid spreading of particles or metal contaminants towards elements formed at the center portion of the wafers.
Japanese Laid-Open Patent Publication No. H7-142449 discloses a technique of limiting discharge planes of upper and lower electrodes of a plasma etching apparatus corresponding to the circumferential surface of the wafer to be etched, and at the same time by blowing an inert gas onto the inner portion of the wafer surface which should not be etched. It is described in this publication that this makes it possible to selectively etch only the circumferential surface of the wafer.
Japanese Laid-Open Patent Publication No. 2001-135712 discloses a vacuum processing apparatus comprising a vacuum chamber in which a wafer is vacuum-processed, a stage disposed in the vacuum chamber and on which the wafer is placed, a plurality of lift-off pins allowed to have a state of being housed in the stage and have a state of being projected upward from the surface of the stage, having an inclined portion inclined so as to allow the upper portion thereof to open outwardly, and a gas blow-out unit blowing a gas upwardly out from the surface of the stage so as to make the wafer float.
Japanese Laid-Open Patent Publication No. H11-186234 discloses an etching apparatus used for plasma-assisted anisotropic etching, configured having a cover provided on a lower electrode so as to cover the region other than a region in which a base is placed, and pressing units pressing the cover onto four divided side faces of the base. The publication describes that the configuration can reduce difference in surface potential between the base and the cover, and can thereby improve uniformity in etching rate of the base.
A problem may, however, arise in that the center of the wafer is misaligned when the wafer is transferred into a processing apparatus, due to a limited accuracy of the transfer system. Any misalignment of the center of the wafer during the etching of the peripheral portion thereof may result in non-uniformity in the width of removal of the peripheral portion, showing a larger width of removal on one side and a smaller width of removal on the other side. It is therefore anticipated that setting of a larger margin for the width of removal of the peripheral portion may result in an etching excessively proceeds into the central area for element formation. On the other hand, setting of a smaller margin for the width of removal so as to avoid excessive etching of the central area for element formation may result in only an insufficient removal of contaminants and so forth in the peripheral portion.
In the etching apparatus selectively etching the peripheral portion of a wafer, stability in the width of removal of the peripheral portion largely affects expansion of a guaranteed area in the peripheral portion. A larger guaranteed area in the peripheral portion can improve the number of obtainable effective semiconductor chips, and can thereby improve the productivity of the chips. It is therefore necessary to improve the stability in the width of removal of the peripheral portion in the peripheral etching.
None of the conventional etching apparatus selectively etching the peripheral portion of the wafer, however, has any mechanism of correcting displacement of the wafer in the reaction chamber. The displacement of the wafer, therefore, directly results in variation in the width of removal of the peripheral portion, and prevents expansion of the guaranteed region in the peripheral portion.